Hitherto, various cooling measures have been employed in semiconductor elements mounted on various electrical appliances such as personal computers and other devices, because if heat generated as a result of driving is accumulated, driving of the semiconductor elements and peripheral devices may be adversely affected. As a method for cooling electronic parts such as semiconductor elements, there are known, for example, a method for mounting the device with a fan to cool the air in the device housing, and a method for mounting the semiconductor element to be cooled with a heat sink such as a heat dissipation fin and a heat dissipation plate.
When a heat sink is mounted on the aforementioned semiconductor element to perform cooling, a thermal conducting sheet is provided between the semiconductor element and the heat sink in order to efficiently dissipate heat in the semiconductor element. As this thermal conducting sheet, a sheet obtained by adding a filler such as a thermal conducting filler in a dispersed state in a silicone resin is widely used. As one example of the thermal conducting filler, carbon fibers are favorably employed (for example, see PTLs 1 to 4).
However, the thermal conducting sheet containing the carbon fibers is excellent in thermal conductivity, but has a problem that electrical conductivity easily becomes high.
Therefore, for the purpose of increasing an insulating property of the thermal conducting sheet, a thermal conducting sheet containing carbon fibers and an electrically insulating heat conductive filler in a specific ratio has been proposed (for example, see PTL 5).
However, this proposed technique has a problem that high thermal conductivity demanded in recent years cannot be obtained.